1. Field of the Invention
The present invention is related to a driving circuit for light emitting diodes, dimmer and method thereof, and particularly to a driving circuit for light emitting diodes, dimmer and method thereof by adjusting a duty cycle of driving current to dim accurately.
2. Description of the Prior Art
Generally speaking, dimming methods of light emitting diodes (LEDs) backlights have two modes, a burst mode and a continuous mode, where the continuous mode is used for adjusting a peak of a driving current of the light emitting diodes. But, operation in the continuous mode may influence optical characteristics of a display, so the burst mode is the main dimming method for light emitting diodes.
The burst mode dimming method controls turning-on or turning-off of driving current of light emitting diodes according to a pulse width modulation (PWM) dimming signal. Luminance of the LED is proportional to an average value of the driving current, which is adjusted linearly by adjusting a duty cycle of the PWM dimming signal. Due to original circuit conditions and design concerns regarding electromagnetic interference, when the driving current is turned on and turned off, the driving current for driving the light emitting diodes exhibits a delay time and a rising time before stabilizing. Please refer to FIG. 1. FIG. 1 is a diagram illustrating a practical average value of the driving current not being equal to an average value of an ideal current due to the delay time and the rising time of the driving current. As shown in FIG. 1, because the practical average value of the driving current is not equal to the average value of the ideal current, a relationship between the practical average value of the driving current and the duty cycle of the PWM dimming signal is nonlinear. Therefore, the prior art can not control accurately luminance of the light emitting diodes and has poorer display quality.